1. Field of Invention
The invention relates to a fan system and a speed detecting device thereof, and, in particular, to a fan system with a low speed alarm function and a speed detecting device thereof.
2. Related Art
With the rapid development of the electronic device toward the high performance, high-frequency, high speed, low weight and small thickness, the temperature of the electronic device is getting higher and higher. Thus, the unstable phenomenon may occur and the product reliability is influenced. Accordingly, the heat dissipation has become one of the most important subjects in the present electronic device.
A fan system usually serves as a heat dissipating structure to keep the electronic device operating normally in the prior art. Referring to FIG. 1, a conventional fan system 10 mainly has a plurality of fans 11 and a plurality of drive chips 12. The fans 11 are connected in series according to the flowing direction of the air. The fans 11 may be connected in series by connecting the fan frames of the fans 11. When any fan 11 breaks down and stops (e.g., when an impeller of the fan 11 is blocked by an object), a corresponding drive chip 12 can detect the condition that the broken-down fan 11 stops rotating, and output a predetermined alarm signal RD (e.g., a high level voltage) to an electronic device 1 so as to alarm that the fan 11 has broken down. Thus, the broken-down fan 11 may be replaced or repaired.
However, because the fans 11 are connected in series, the broken-down fan 11 may rotate due to other fans. Thus, the drive chip 12 corresponding to the broken-down fan 11 cannot detect the broken-down condition and make a misjudgment such that the alarm signal RD cannot be outputted.
Therefore, it is an important subject to provide a fan system and a speed detecting device thereof capable of solving the above-mentioned problems.